very slow twist

[George]

Not sure we are playing in the same league, but I'll ask...what kind of spin are you describing? Does the 'kicker' impart spin around the center line of the ball just the way normal rifling does?

Spence

 

[BrownBear]

No idea of how much spin is applied, but there's also no way the spin is oriented along the axis of ball flight. Couldn't be. It has to be spinning 90 degrees to the ball path rather than around it.

I reconciled it all in my mind when I heard/read discussion of the spin stabilizing a ball along its path by gyroscopic action, just as a spinning gyroscope is pretty good at moving straight and true along one course, but resists deviation like crazy. That's why they use gyroscopes in some navigation equipment. It was easy to measure forces and vectors as the gyro resisted movement off it's course, or its stable position.

Frankly I've heard lots more about that from navigators than from ballisticians, but when the ballistics types started talking gyro's, it rang true with what the navigators were saying.

I did a quick googlectomy on ballistics and found a couple of wiki points that might help:


Stabilizing non-spherical projectiles during flight

Two methods can be employed to stabilize non-spherical projectiles during flight:

Projectiles like arrows or sabots like the M829 Armor-Piercing, Fin-Stabilized, Discarding Sabot (APFSDS) achieve stability by forcing their center of pressure (CP) behind their center of gravity (CG) with tail surfaces. The CP behind the CG condition yields stable projectile flight, meaning the projectile will not overturn during flight through the atmosphere due to aerodynamic forces.
Projectiles like small arms bullets and artillery shells must deal with their CP being in front of their CG, which destabilizes these projectiles during flight. To stabilize such projectiles the projectile is spun around its longitudinal (leading to trailing) axis. The spinning mass makes the bullet's length axis resistant to the destabilizing overturning torque of the CP being in front of the CG.

Gyroscopic drift (Spin drift)

Gyroscopic drift is an interaction of the bullet's mass and aerodynamics with the atmosphere that it is flying in. Even in completely calm air, with no sideways air movement at all, a spin-stabilized projectile will experience a spin-induced sideways component. For a right hand (clockwise) direction of rotation this component will always be to the right. For a left hand (counterclockwise) direction of rotation this component will always be to the left. This is because the projectile's longitudinal axis (its axis of rotation) and the direction of the velocity vector of the center of gravity (CG) deviate by a small angle, which is said to be the equilibrium yaw or the yaw of repose. The magnitude of the yaw of repose angle is typically less than 0.5 degree.[36] Since rotating objects react with an angular velocity vector 90 degrees from the applied torque vector the bullet's axis of symmetry moves with a component in the vertical plane and a component in the horizontal plane; for right-handed (clockwise) spinning bullets, the bullet's axis of symmetry deflects to the right and a little bit upward with respect to the direction of the velocity vector as the projectile moves along its ballistic arc. As the result of this small inclination, there is a continuous air stream, which tends to deflect the bullet to the right. Thus the occurrence of the yaw of repose is the reason for the bullet drifting to the right (for right-handed spin) or to the left (for left-handed spin). This means that the bullet is "skidding" sideways at any given moment, and thus experiencing a sideways component.[37][38]

The following variables affect the magnitude of gyroscopic drift:

Projectile or bullet length: longer projectiles experience more gyroscopic drift because they produce more lateral "lift" for a given yaw angle.
Spin rate: faster spin rates will produce more gyroscopic drift because the nose ends up pointing farther to the side.
Range, time of flight and trajectory height: gyroscopic drift increases with all of these variables.
density of the atmosphere: denser air will increase gyroscopic drift.


There's lots more here and that's just the tip of the gyroscoptic iceberg.

If that's not enough to spin your head like a gyroscope here is another discussion of gyroscopic effect on bullet flight.

Here's a quick excerpt:

The spinning motion, induced by the rifling of the barrel, keeps the bullet stable because of gyroscopic effect. This effect limits, or cancels, the destabilizing momentum. It is the same effect that you can observe playing with a spinning top that prevents the toy from falling on its side””due to gravity””while it’s spinning. The higher the destabilizing momentum, the highet the gyroscopic forces must be to keep the bullet stable. The gyroscopic force is a function of the spin rate: the higher the spin, the higher the gyroscopic stabilizing force. Thus, bullets with longer destabilizing momentum levers need higher spin rates.

The spin rate of the bullet depends on the barrel twist rate, and on the muzzle velocity. The twist rate is the number of twist that the barrel rifling does in a given space. On rifles specification it is usually indicated the distance that a rifling take to make a full twist, in example 1:10 indicate that the rifling make a full twist every ten inches. Obviously, the shorter the twist rate, the higher is the spin rate. Given a twist rate, the higher is the muzzle velocity, the higher is the spin rate.

 

[George]

If the spin is oriented perpendicular to the line of flight, the sphere will curve, not fly in a straight line. Robins demonstrated that rather dramatically with musket balls in early 18th century. I used to play a lot of pingpong, and with that lightweight ball you can make the thing miss the target by two feet in the length of the table. Sounds as though your nephew is using something like that. With a heavy sphere and spin along the horizontal axis, I don't see the similarity.

Spence

 

[George]

Just like the guys that use to cheat in smoothbore matches with partially rifled smoothbores...

Did they really cheat, or did they just think they did? Did they always outshoot the honest shooters?

Spence

 

[BrownBear]

If the spin is oriented perpendicular to the line of flight, the sphere will curve, not fly in a straight line. Robins demonstrated that rather dramatically with musket balls in early 18th century. I used to play a lot of pingpong, and with that lightweight ball you can make the thing miss the target by two feet in the length of the table. Sounds as though your nephew is using something like that. With a heavy sphere and spin along the horizontal axis, I don't see the similarity.

Spence

Ah, but if you're sights are set right it curves accurately along the same arc, hitting the same place (more or less) each time. Same thing happens due to gyroscopic spin out of a rifled barrel at longer ranges, as shown in the correction tables for artillery and long range riflery. They talk about it in one of those pieces I pulled out for you.

My nephew's "monkeying" with kickers and where they are located around the axis of the barrel has all to do with how they arc- up, down, left or right. His favorite long range "rifle" actually has the kicker located so the ball rises due to spin. Dunno about that, because my only evidence is watching him shoot.

From my days pitching fast-pitch softball, I know how to throw a rise ball. You don't hear about those in baseball though, cuzz you can't throw them with the overhand (or sidearm) motion. Sure a lot of talk about "sinkers" and curves though. It's all about the spin on the ball, whether out of a barrel or a calloused hand.

 

[coloradoclyde]

Here's some visual aid for gyroscopic precession

https://youtu.be/ty9QSiVC2g0

https://youtu.be/GeyDf4ooPdo

 

[George]

It's all about the spin on the ball, whether out of a barrel or a calloused hand.

But we are talking about balls spinning on an axis coincident with the line of flight. Your nephew's shooting, the up-rise soft ball, etc., are very different than that.

Compare a ball spinning along that horizontal axis and one not spinning at all, that's the difference being considered.

Spence

 

[coloradoclyde]

op:

 

[BrownBear]

It's all about the spin on the ball, whether out of a barrel or a calloused hand.

But we are talking about balls spinning on an axis coincident with the line of flight. Your nephew's shooting, the up-rise soft ball, etc., are very different than that.

Compare a ball spinning along that horizontal axis and one not spinning at all, that's the difference being considered.

Spence

Same affect I think, but with the rise, left/right, drop along a predictable axis. The gyro effect makes them do it consistently, and you can adjust sights for consistency. With no spin and a "knuckleball" effect, it's not so predictable or "accurate." That's why catchers use oversize mitts when looking at a knuckler on the mound. The rise, left/right, drop can be quite consistent and no large mitt required with a good pitcher. In fact, that's how you throw a knuckleball---- no spin at all, so it kinda floats and wanders all over the place at it approaches the batter.

Of course, on off days when I was pitching, there wasn't a mitt big enough to hunker behind the plate for me! :rotf:

 

[coloradoclyde]

Can you throw a perfectly smooth ball and make it rise or fall like a softball?.... op:

 

[M. De Land]

You need stitching on the ball to make that happen.
Concerning slow twist, I made a percussion pistol of .54 cal with a rifle barrel having a pitch of 1 in 60 and it is superbly accurate to the 50 yards I've tested it.
Round balls just don't need much spin velocity to shoot straight.

 

[coloradoclyde]

You need stitching on the ball to make that happen.
Concerning slow twist, I made a percussion pistol of .54 cal with a rifle barrel having a pitch of 1 in 60 and it is superbly accurate to the 50 yards I've tested it.
Round balls just don't need much spin velocity to shoot straight.

Exactly!....

 

[excess650]

Forsythe style rifling has wider grooves than lands and is relatively shallow. He was a proponent of slow twists, large bores, and heavy powder charges for extending range with PRBs. Twists as slow as 1-144" come to mind. My Moody made barrel was cut .62 x 1-90", but I haven't gotten around to finishing that project.

I've read that original Jaegers were typically rifled 1 turn in the length of the barrel, so figure in the 24-36" range, and normally bores exceeding .54 on up through .75.

My .62 Jaeger weighs 7-1/2#, has 1-66" twist, and groups as well with 100gr fffg as it does with 120gr fffg. Neither makes excessive recoil, but I'm sure that the 2" x 5" buttplate helps. At 140gr it gets to be noticeable.

 

[George]

Can you throw a perfectly smooth ball and make it rise or fall like a softball?.... op:

Yes, you can. There are no seams on a pingpong ball.

Spence

 

[Rifleman1776]

I've read that original Jaegers were typically rifled 1 turn in the length of the barrel,

That is simply another Jaeger myth. :nono:

 

[Rifleman1776]

When I got into BP shooting in the 1970s the accepted dogma was that slow, deep rifling was the best for round ball shooting, because a round ball doesn't need much stabilization.

As you say "dogma". Haven't looked up the word in a dictionary, but methinks it is sorta synomyous with another 'dog (stuff)' word.
But, still today a lot of shooters, particularly bench rest guys believe it.
Part of their desire for the slow twists and super-super heavy charges is an attempt to gain high velocities to buck the wind. At one envent I attend one bencher has a caliber so big and charges so incredible it literally shakes the earth and knocks equipment off tables and benchs 40 feet away. :shocked2:

 

[George]

Haven't looked up the word in a dictionary, but methinks it is sorta synomyous with another 'dog (stuff)' word.

Dogma:

3. prescribed doctrine proclaimed as unquestionably true by a particular group:

4. a settled or established opinion, belief, or principle:

Our hobby is full of them, and occasionally one of them is true. :grin:

Spence

 

[nkbj]

Long range heavy ball, barrel long enough, slow twist to minimize spin drift as well as cleaning problems...
the Baker was a nice package!

All reasons why I like The Rattler, my TC flinter Hawken with its 32" rifled .62 caliber barrel.

But I think I'm gonna like the .52 flinter Renegade with 28" twist as well.
:wink:

 

[coloradoclyde]

Can you throw a perfectly smooth ball and make it rise or fall like a softball?.... op:

Yes, you can. There are no seams on a pingpong ball.

Spence

Fantastic!.....Now tell me why you can do it with a pin pong ball but not a steel ball bearing..... op:

 

[George]

Fantastic!.....Now tell me why you can do it with a pin pong ball but not a steel ball bearing..... op:

Steel ball bearing?

Does not compute.

Spence